Reheating Coffee: Everything You Should Know


This is a guest post from Craft Coffee Spot about reheating coffee, without it tasting bad. If you’re wondering if you can reheat your coffee without it tasting overly bitter, or how to reheat coffee in the microwave without altering the taste, this post is for you.

We’ve all had times when coffee has gone cold.  Maybe you were in a rush and didn’t have time to finish, or maybe you made some extra coffee earlier. Is it ok to reheat coffee? 

In general, I’d say avoid it since coffee gets more bitter with additional heat.  However, you can make coffee warm and quite drinkable again if you use low heat and only warm coffee to 60 °C (140 °F).

Coffee is a complex substance with a good amount of science behind coffee and heat.  I reviewed the research behind this and how reheating will make your coffee more bitter – unless you follow certain steps.

I’ll discuss these aspects in this article and the do’s and don’ts to reheat coffee properly. Continue reading below to find out more.

The Science Behind Heat And Coffee

Before we jump into reheating coffee, we need to understand the chemistry behind heat and coffee. Heat changes the composition of green coffee beans during the roasting and brewing process, which impacts coffee’s flavor and bitterness.

A green coffee bean has over 1,000 different compounds.  The compounds are generally of two types.  First is the non-volatile compounds, which include caffeine and chlorogenic acids.  Second is the volatile compounds, which contribute flavor and aroma notes that make great coffee.

Heat breaks down non-volatile compounds during the roasting process and effectively creates many of the volatile compounds that we cherish in our coffee. The problem is the volatile compounds are, let’s say, volatile and tend to burn off as coffee roasts longer.

So the longer the coffee roasts, the more those unique flavor notes tend to disappear in favor of other tastes.  That is why light roasts have a more distinct taste and aroma from volatile compounds, while dark roasts have a roasted and burnt taste.

Brewing coffee leads to another round of changes in the chemical composition of coffee.  The hot water extracts certain coffee compounds into our cup, and good coffee brewing is about extracting the good compounds (namely, volatile compounds) while avoiding others. 

Too much heat will over extract compounds that we don’t want, like chlorogenic acids, which is why proper water temperature is so important for brewing coffee. 

Those chlorogenic acids cause the bitter taste in our coffee.  Some chlorogenic acids degrade during roasting or change into flavorful sugars during the Maillard reaction.  However, most chlorogenic acids stay in the bean and get extracted during brewing.  With enough heat, chlorogenic acids break down into caffeic acid, which is directly responsible for bitter or astringent taste in coffee.

But What Does This Have to Do with Reheating Coffee?

The science behind roasting and brewing your original cup still holds when you reheat coffee.  When you reheat coffee that has gone cold, you are effectively doing another round of brewing without the fresh grounds.  

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Said differently, the beans you use to make your coffee contain acids, compounds, and oils. During the original brewing, these were released in a calculated way to account for the taste that we all look forward to when enjoying coffee.

During the reheating process, the oils, acids, and compounds become exposed to an additional form of brewing. This extension can release oils and acids that cause a bitter taste, like caffeic acid.  Reheating coffee also burns off the volatile compounds that contribute most flavor, while more chlorogenic acids convert into bitter-tasting caffeic acids.  

The additional heat leads to more good stuff going away while the bitter stuff becomes more prevalent.  That’s why an old pot of coffee tastes so terrible after it sits on the burner for hours.

For all these reasons, you should avoid reheating coffee.  Applying more heat to brewed coffee will only make it more bitter and affect the taste.  Even leaving coffee out to cool naturally will lead to worse flavor.

How to Properly Reheat Coffee

While we’ll always recommend brewing coffee with the freshest beans and consuming it straight away, we know that is not always possible.  Some situations may warrant a reheat of your morning cup. 

To reheat coffee properly, use the minimum heat necessary to bring coffee to a warm temperature.  This avoids the negative chemical reactions as much as possible.

Use a low temperature to heat coffee evenly.  Also, heat coffee to a modest temperature of 60o C (140o F).  This temperature is lower than a freshly brewed coffee, which usually comes out around 75o C (167o F).  A low temperature mitigates most of the chemical changes, and we’ve even found most people prefer a temperature of 60o C (140o F), and it brings out the best flavor in coffee.

Here are two specific ways to reheat coffee while appropriately preserving the taste and flavor.

Reheating Coffee by Stove

If you notice that your coffee is running cold, don’t fret. One of the best ways to get it back to good is by reheating it on the stove. Simply follow these straightforward steps:

  • Pour the coffee from the mug into a small pot.
  • Heat coffee until it steams. Do not allow the coffee to boil.
  • Next, pour your coffee back into a cup (preferably not porcelain, as the newly warmed coffee may cause the cup to be too hot to hold).

This avenue for warming your beverage will keep the compounds and oils intact and reduce the acids from making your drink bitter. However, you have to perform this method promptly. If you try to reheat your coffee after it has been brewed for an hour and a half and sitting out in a mug, you are likely to have an unpleasant taste.

Reheating Coffee by Microwave

Using a microwave to reheat your coffee is another option. However, going this route requires you to change a few settings on your machine to preserve the quality of your brew. 

In order to best reheat your coffee with a microwave, follow these steps:

  • Set your microwave power to 80% (or medium)
  • Place your microwave-safe mug inside
  • Heat your coffee at 30-second intervals, checking the temperature after each cycle
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Going by 30-second intervals allows you to reduce the chances of burning your beverage. While reducing the power also decreases the circumstances of the drink turning bitter, it is still possible that it can happen.

To combat the bitter taste that can come from microwave heating, many people mask the flavor by later adding creamer, milk, or half and half.

What Not to Do When Reheating Coffee

While there are specific things you need to do when reheating a cup of coffee that has gone cold, there are also particular things that you should not do. These include:

Avoid Reheating Dairy

If you add milk or creamer to sweeten your coffee after brewing it, it is not wise to reheat your beverage. Dairy and creamer add different components to a drink and can clot easily. Additionally, heating dairy can bring a scalding, unpleasant taste to your coffee. 

Another note to remember is that the length of time your cup of coffee will still taste good decreases when you incorporate dairy or creamer. Dairy often goes back when exposed to warm conditions outside of the refrigerator. Therefore, reheating or drinking dairy that has been out for a long time can cause digestive issues or health concerns.

Don’t Microwave at Full Power

When you use a microwave, it does its job fast. This action doesn’t change when you are reheating coffee. Therefore, having your microwave at full power when warming up your drink will cause it to heat up more rapidly than you desire.

When your coffee gets too hot, too quickly, it can experience burning. If you have ever had burnt coffee, you know why it’s not a pleasant taste and the reason you should avoid it at all costs. 

Don’t Use an Extended Warmer on Your Machine

Many coffee machines come with a setting that keeps your brewed pot of coffee warm for several hours after you’ve started your brew. However, even though you may deem this helpful or convenient, it isn’t a good choice.

When your coffee remains heated for that long, it will lose the integrity of its taste. Just like when you’re deciding which coffee bean grind to use based on fast or slow flow, heating your brewed coffee for that long gives it more extended access to water flow and increases the chance of bitterness.

While the brewing process doesn’t involve coffee grounds going directly into the coffee pot, some particles make their way into the coffee. You can see this every so often when you get to the bottom of the pot or use a French press.

Those particles are what continue to brew when you leave your machine on warm. Therefore, the extended brewing will bring about the bitterness and scalding flavors you want to avoid. 

How to Avoid Cold Coffee

Outside of using the warming mechanism on your coffee-making machine or continually reheating your drink, some options can keep your drink fresh without worrying about affecting the taste.

Brew Small Batches

There are many ways to brew coffee now that don’t require you to make a whole pot at a time. Whether it is an individual cup on a drip machine, French press, pour-over, there are many options for creating a drink in a single serving amount.

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When you do this, you have access to fresh coffee without the fear of having the extra coffee that is still sitting in the pot lose its perfect taste. What’s more, if you decide you want another cup, you can always make another one of the same size and amount and instantly have another mug of hot, delicious java!

To learn more about the V60 pour-over coffee maker see:

V60 pour-over Coffee maker review

Thermal Cups

This suggestion may seem like a no-brainer, but many people don’t think about it when drinking coffee at home. Most households have some type of travel coffee cup, but they choose to reserve it for the sole purpose of being on the go and mobile. Therefore, people don’t think to use it when consuming coffee at home.

However, using a thermal cup at home will allow your drink to stay warm much longer than a standard mug will. The insulation in these styles of cups keeps the heat inside without concern of over-brewing. Because the cup itself is not a heat source, you don’t have to worry about particles causing bitterness in your drink. 

for more information on leakproof travel mugs see:

Best leakproof travel mugs

Switch to Iced Coffee

While some people are not fans of cold coffee, there is an entire population of coffee drinkers who can’t go without their iced coffee. Because of that, iced coffee, cold brew, and frappuccinos are rising in popularity. 

The nice part about iced coffee is that you don’t have to worry about the drink turning cold – because it already is! Additionally, the inclusion of ice keeps it in the same state for a while, unless, of course, you are in the middle of summer. 

While iced coffee isn’t everyone’s favorite, you and your favorite barista can often make it in the same flavor styles as warm coffee. If you find yourself constantly needing to reheat coffee, you might consider giving iced coffee a try. You might surprise yourself and like it!

Final Thoughts

Coffee botherers want to have a great cup of coffee every time.  However, enjoying the drink thoroughly takes a bit of planning and effort.  Sometimes, coffee that you’d still like to enjoy has gone cold, and you don’t always need to throw out the last cup either. 

You can successfully reheat your coffee via stovetop or microwave, but make sure to use low heat and avoid heating coffee above 60 °C (140 °F).  Consider a thermal mug or a mug warmer to avoid reheating coffee altogether.

About the Author

Marko Lazarevic is the founder of Craft Coffee Spot.

He has been trying new single-origin blends and different brewing methods since stumbling upon a Kalita Wave during his first job. 

Marko shares the best methods through coffee brewing guides. His favorite brewing device is a French press.


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